Researchers found that symbiotic phytoplankton capable of fertilising the ocean with nitrogen ‘fertilizer’ evolved back in the Cretaceous at a time when the oceans were nutrient deprived. The cyanobacterium which the researchers have discovered is unique because it has no photosynthetic capabilities – a trait commonly associated with these microorganisms. Instead, its sole purpose is to provide nitrogen to a more complex cell host.
This ‘slaving event’ evolved around 90 million years ago towards the end of the Cretaceous period, when the oceans were starved of nutrients. While nitrogen is hugely abundant in the atmosphere, most organisms can’t breathe nitrogen, instead relying on bacteria to transform atmospheric nitrogen into bioavailable nitrogen – critical for growth and survival in the marine food web.
New finding identified the intimate relationship of this marine nitrogen factory which is formed by a single-celled alga (prymnesiophyte) and the cyanobacterium UCYN-A. A stage of scarce nutrients in the ocean could have led to the establishment of the symbiotic relationship between the algae and the cyanobacteria back in the late Cretaceous, after the oceans had been deprived in nutrients.
This study, which used data from the Tara Oceans circumnavigation expedition, is published in Nature Communications today [22 March].
— source bristol.ac.uk